Apparatus for shaping melts comprising inorganic oxides or minerals with an improved heating device

ABSTRACT

Fibers, pipes, rods, strips or profiles made of high-melting inorganic oxides or minerals are used in great quantities, for example for reinforcing plastics, ceramics and metals. In order to produce said products, use is made of apparatuses comprising a melt container with an individual orifice, or orifice plate with a multiplicity of orifices, arranged in the base of the melt container. The melt in the melt container has to be kept at as homogeneous as possible an operating temperature above the individual orifice or orifice plate. For this purpose, the melt container is usually heated by a direct through flow of current. This results in high radiation losses to the surroundings and to a correspondingly high need for electric energy. It is proposed, for the heating of the melt, to arrange one or more pipes in the melt container, the pipes having at least one connection to the outside through the container casing, and electric heating elements being inserted into the pipes. This type of heating results in a homogeneous temperature distribution of the melt above the individual orifice or the orifice plate and permits an energy saving of more than 50%.

REFERENCES TO A RELATED APPLICATION

This application claims the benefit of co-pending application 61/060,692filed Jun. 11, 2008 and German patent application DE 10 2007 061 695.5filed Dec. 19, 2007 which is relied on and incorporated herein byreference.

INTRODUCTION AND BACKGROUND

The invention relates to an apparatus for shaping melts comprisinginorganic oxides or minerals, in particular for producing glass fibersand basalt fibers. The apparatus contains a melt container with acontainer casing and an individual orifice or orifice plate arranged inthe base of the melt container.

Fibers, tubes, rods, strips or profiles made of high-melting inorganicoxides or minerals are produced in large amounts. Fibers from saidmaterials are used, for example for reinforcing plastics, ceramics andmetals.

An early apparatus for the production of glass threads is shown in thepatent publication GB 361,220. The cylindrical heating chamber is madefrom refractory material, such as burnt fireclay or heat resisting metalalloy, and along one side is provided with one or more spinning nozzlesthrough which the glass can be withdrawn from the chamber. Within theheating chamber is arranged a plurality of heating elements parallel tothe cylinder axis. Each consists of a tube manufactured from porcelainor heat resisting metal alloys having arranged on their inner surface anelectrical resistance. This apparatus, due to the preferred use of burntfireclay and porcelain, cannot cope with today's quality requirementsand the required diversity of raw materials for the fibers. In case theapparatus is manufactured from refractory metal alloys the heatingcurrent will flow through the whole apparatus because heating element,resistance and heating chamber form an integral unit.

The today's apparatuses for manufacturing glass fibers or mineral fiberspredominantly consist of alloys of the platinum group metals and areheated by direct current flowing through the casing of the apparatus.Such apparatuses contain a melt container with an individual orifice ororifice plate arranged in the base of the melt container. The meltcontainer may be a tub, a trough, a cone, a cylinder or the like.

The melt in the melt container has to have as homogeneous as possible atemperature distribution above the individual orifice or orifice plateso that fibers, without disturbances of the drawing process, can bedrawn from all of the shaping orifices having the same fiber crosssection. An orifice plate can be equipped with several hundredindividual orifices for shaping fibers. Apparatuses with an orificeplate are shown in laid-open specifications DE 196 38 056 A1, US2003/0145631 A1 and US 2003/09041627 A1; an apparatus with an individualorifice is described in DE 10108 831 C1.

The inorganic oxides or minerals are melted in a furnace using knownmethods and are introduced into the apparatus. In the case of remeltprocesses, the apparatus is connected directly to the furnace; indirect-melt processes, the apparatus is fixedly connected to adistributor channel. Metals, in particular platinum and platinum alloys,are usually used as the materials for the apparatus and for the orificeplate and orifices. Because of the high thermal conductivity of themetals, the apparatus is insulated against heat loss in order to ensurea constant viscosity of the melt and as homogeneous as possible atemperature distribution above the individual orifice or orifice plate.By contrast, the individual orifice or the orifice plate in the base ofthe melt container cannot be thermally insulated, and therefore transferof heat convection and radiation of heat to the colder surroundingsoccur. The heat loss is usually compensated for by a higher operatingtemperature of the melt and by direct electric heating of the metallicapparatus and thus results in a high energy consumption. As aconsequence of the heat loss to the surroundings, there is a temperaturegradient and, associated therewith, a viscosity gradient in the melt.

SUMMARY OF THE INVENTION

It is the object of the present invention to specify an apparatus forshaping melts comprising inorganic oxides or minerals, the apparatushaving a more homogeneous temperature distribution in the melt and asignificantly reduced energy consumption than conventional apparatusesof this type.

This object is achieved by means of an apparatus (1) for shaping meltscomprising inorganic oxides or minerals, the apparatus containing a meltcontainer (2) with a container casing (3, 4) and an orifice plate (7)with a plurality of orifices (8), or an individual orifice, arranged inthe base (6) of the melt container. In the apparatus, one or more pipes(9) are located in the melt container. The pipes having at least oneconnection/opening to the outside through the container casing, andwherein electric heating elements (10) are inserted into the pipes. Themelt container (2), the individual orifice or orifice plate (7) and thetubes (9) are manufactured from platinum, palladium or alloys thereofwith one or more metals selected from rhodium, iridium and gold.

The heating elements or heating cartridges may be commercially availableheating elements which can be obtained e.g. from the company Kanthal forworking temperatures up to 1850° C. It is essential for the inventionthat the heating elements are electrically isolated from the tubes inwhich they are inserted. Contrary to GB 361,220 the apparatus accordingto the invention is not heated by direct current flowing through thecasing of the melt container.

According to the invention, the temperature of the melt is kept at anoperating temperature with the aid of the heating elements inserted intothe pipes. The heat source for heating the melt is therefore placeddirectly into the melt. The heat is delivered to the melt by thermalconduction and radiation of heat. As a result, in comparison to thedirect heating of the metallic apparatus, the heat losses of the heatingsystem to the surroundings are reduced by more than 50%. Bus bars arealso no longer required for introducing the current into the metallicapparatus, and therefore precious metal can be saved. In addition, theapparatus according to the invention makes it possible for thetemperature of the melt to be easily adjusted.

The apparatus is suitable both for an orifice plate with several hundredorifices and also for individual orifices. In the first case, the meltcontainer has a rectangular base surface and is delimited by four sidewalls. In this case, it is advantageous if the pipes together with theheating elements are guided between two opposite container walls and aplurality of such pipes are arranged parallel to one another. Such anapparatus is suitable for the mass manufacturing of technical fibersfrom glass or minerals. If, by contrast, container glass and high-gradetechnical glass are to be formed, then it is expedient to use anapparatus with just a few orifices or just one individual orifice. Themelt container is then in the form of a pot, cone or cylinder. In thiscase, the pipe for heating the melt can be designed as a closed circularpipe. The heating pipe is therefore matched to the internal geometry ofthe melt container. A supply pipe leads from the outside through thecasing of the melt container and is connected to the circular pipe. Theheating element is inserted into the circular pipe via the supply pipeand is supplied with electric energy.

The container casing of the apparatus, the individual orifice or theorifice plate and the pipes are manufactured from platinum, palladium oralloys of said platinum metals with one or more of the metals rhodium,iridium and gold. In order to satisfy more high temperature strengthrequirements, the platinum or the platinum alloy can be stabilized byoxidic material finely distributed in the metal. Zirconium oxide andyttrium oxide are particularly suitable for stabilization purposes. Theheating pipes are welded to the container casing so as to provide a sealagainst the melt escaping.

BRIEF DESCRIPTION OF DRAWINGS

The invention is explained in more detail with reference to an exemplaryembodiment and FIGS. 1 to 6, in which:

FIG. 1 shows a cross section through an apparatus according to theinvention with an orifice plate and several hundred orifices

FIG. 2 shows a view from above of the apparatus from FIG. 1

FIG. 3 shows an apparatus as in FIG. 1 with a ceramic bushing block tothe forehearth channel and ceramic insulating compound

FIG. 4 shows an apparatus with an individual orifice

FIG. 5 shows a perspective view of an apparatus with an orifice plateand several hundred orifices without a covering sieve

FIG. 6 shows a perspective view of the apparatus from FIG. 5 with acovering sieve.

DETAILED DESCRIPTION

FIG. 1 shows a cross section through a particular embodiment of theapparatus (1) according to the invention. The apparatus comprises themelt container (2) with a container casing (3, 4) and a circumferentialflange (5) which encircles it on the upper side and is intended forfixing the melt container to a forehearth channel. An orifice plate (7)with the orifice openings (8) is embedded in the base (6) of the meltcontainer. The orifice openings may be simple through boreholes ordeep-drawn orifices or else separately manufactured orifices. Duringoperation, the entire interior of the melt container is filled with themelt. Above the orifice plate, in this embodiment of the apparatus,through pipes (9) are arranged between two opposite sections of thecontainer casing (3, 4) and are guided through the container casing.Said pipes are preferably provided with a round cross section, but mayalso have any other expedient cross-sectional shape. Electric heatingcartridges (10) with the connecting wires (11) guided outward areinserted in said pipes. To maintain the operating temperature of themelt, the heating cartridges are supplied with electric current. FIG. 2shows a view from above of the apparatus from FIG. 1. The same referencenumbers denote the same elements as in FIG. 1.

FIG. 3 shows an apparatus, the melt container (2) of which is integrallycast in a ceramic insulating compound (23) for the purpose of heatinsulation. The forehearth channel (20) is arranged directly above theapparatus. The longitudinal extent of the forehearth channel shown inFIG. 3 is perpendicular to the plane of the drawing. A further ceramicbrick or bushing block (22) serves as the adapter block and for heatinsulation. The forehearth channel (20) is filled to the level (21) witha melt. The melt passes from a furnace via the forehearth channeldirectly into the apparatus. The melt container (2) is completely filledwith the melt. As in FIG. 1, the apparatus is equipped with throughpipes (9). The through pipes are guided through bores in the ceramicembedding compound (23).

FIGS. 1 to 3 show embodiments of the apparatus with a multiplicity oforifices (8).

By contrast, FIG. 4 shows an apparatus with just one individual orifice(8) for shaping container glass and high-grade technical glass. FIG. 4a) shows a cross section through the apparatus while FIG. 4 b) shows aview of the apparatus in the direction of the arrow A. For heatingpurposes, the melt container (2) contains a pipe (9) which is bent andjoined together to form a circular ring. The circular pipe is connectedto a feed pipe (12) which is guided through the container casing (3) andis welded thereto and permits a heating element to be inserted into theheating pipe (9). Reference number (13) denotes the orifice bore whichis visible from above.

FIG. 5 shows an apparatus according to FIG. 1 in a perspective view. Thearrangement of the through pipes (9) can be seen clearly. FIG. 6 showsthe same illustration as in FIG. 5, but with a sieve covering (30) overthe through pipes. The sieve among other things has the task ofcollecting undissolved particles occasionally contained in the melt andof thereby preventing the orifices from becoming clogged.

Example

The temperature distribution within the apparatus according to FIG. 1and the temperature profile under the orifice plate for conventionaldirect heating and for the heating according to the invention by meansof the heating cartridges inserted into the through pipes have beendetermined with the aid of simulation calculations. The calculationswere based on an apparatus having the following dimensions: length=510mm; width=160 mm; height=50 mm; sheet-metal thickness=1.5 mm. It wasassumed that the apparatus was equipped with 2400 orifices having aclear diameter of 2 mm. Such an apparatus is capable of spinning 1500 kgof glass per day to form glass fibers with a diameter of 13 μm. Thecalculations were made using the known thermal properties of platinum,glass and ceramic. The table below lists the material data used:

TABLE Material data used for the simulation calculations CeramicPlatinum Glass Density g/cm³ 1.4 21.45 2.63 Thermal 3 71.6 0.8conductivity W/mK Heat capacity J/kg 800 130 800 K Emissivity 0.42-0.260.036-0.192 0.95-0.85 (499-826° C.) (RT-1.226° C.) (260-540° C.) RT =room temperature

The simulation calculations supplied the following result:

During conventional, direct heating of the apparatus, a heating power of21 kW is required in order to keep the melt at an operating temperatureof 1125° C. A large part of the thermal energy introduced into theorifice plate by the resistance heating is radiated directly downward.If, by contrast, the same heating power is introduced directly into theglass melt via the through pipes, then the temperature of the meltincreases just above the orifice plate to more than 1400° C. Duringconventional heating, the melt within the melt container already has asharp temperature drop from the upper edge to the orifice plate. In thecase of the heating according to the invention, this temperaturegradient is virtually nonexistent. Furthermore, during conventionaldirect heating of the metal apparatus, a lateral temperature gradientwith a temperature drop from the outside to the center is obtained. Inthe case of heating according to the invention, this temperaturegradient is virtually nonexistent too.

With the same input of energy as in conventional heating, the heatingaccording to the invention therefore results in more uniform heating ofthe melt. Heat is now transferred directly from the heating sourcethrough the pipes to the melt and finally to the melt container with theorifice plate. The heat is therefore not radiated directly to thesurroundings. However, because of the smaller heat losses during heatingaccording to the invention, the melt heats up much too severely, andtherefore the amount of heat supplied has to be reduced. Only with areduction of the heating power to 3.9 kW were approximately identicaltemperature conditions as during conventional heating at 21 kW obtained.The heating according to the invention therefore permits the input ofenergy in order to maintain the operating temperature of the melt to bereduced to approximately one fifth.

Of course, the indirect heating according to the invention of theapparatus can be used not only in the case of apparatuses having amultiplicity of orifices, but can advantageously also be used in thecase of individual orifices.

The apparatus is preferably used for producing fibers, tubes, rods,strips or profiles made of high-melting inorganic oxides or minerals.

1. An apparatus (1) for shaping melts comprising inorganic oxides orminerals, the apparatus containing a melt container (2) with a containercasing (3, 4) and an individual orifice, or orifice plate (7) with aplurality of orifices (8), arranged in the base (6) of the meltcontainer, wherein one or more pipes (9) are located in the meltcontainer, the pipes having at least one connection to the outsidethrough the container casing, and wherein electric heating elements (10)are inserted into the pipes and the melt container (2), the individualorifice or orifice plate (7) and the tubes (9) are manufactured fromplatinum, palladium or alloys thereof with one or more metals selectedfrom rhodium, iridium and gold.
 2. The apparatus as claimed in claim 1,wherein the pipes (9) together with the heating elements (10) arearranged between two opposite sections of the container casing (3, 4)and are guided through the container casing.
 3. The apparatus as claimedin claim 2, wherein the precious metal or the precious metal alloy isstabilized by oxidic material finely distributed in the metal.
 4. Theapparatus as claimed in claim 1, wherein 1 to 25 orifices per squarecentimeter are embedded in the orifice plate (7).
 5. The apparatus asclaimed in claim 1, wherein only one individual orifice is present inthe base (6) of the apparatus.
 6. The use of the apparatus as claimed inclaim 1 for producing fibers, pipes, rods, strips or profiles made ofhigh-melting inorganic oxides or minerals.